Last January Sea-Watch 3 picked up 47 migrants who then had to spend 12 days at sea before being allowed to disembark at Catania in Sicily after a deal was struck with several European countries to take them in.

Salvini called for the ship to be seized for aiding clandestine immigration and the vessel was blocked for three weeks in Catania before being allowed to leave without charges.

Sea-Watch 3 went on to Marseille in France and ended up blocked in the port for three months as it battled attempts in the Netherlands to limit its work.

The vessel finally sailed again on Saturday with the non-profit organisation saying it was now the only civilian rescue ship in the central Mediterranean as other charity vessels remain caught in administrative and legal red tape.

Over 60 migrants rescued at sea by the Italian navy and a charity ship disembarked in Italy last Friday, despite Salvini's "closed ports" policy, while three died and dozens more went missing after another migrant boat capsized off Tunisia

Rome's populist government has taken an increasingly hard line on migration, and Salvini, head of the anti-immigrant League party, last month banned charity vessels from rescuing migrants off Libya.

Charity ships have drawn fire from Rome by attempting on occasion to stop migrants being taken back to crisis-hit Libya, which human rights organisations say is not safe for repatriations